An anatomical study of the lumbar external foraminal ligaments: appearance at MR imaging

A comparative study of the anatomy and MRI images of the lumbar foraminal ligaments at the L1-L5 levels

PURPOSE

The purpose of this study was to evaluate the ability of MRI images to reveal foraminal ligaments at levels L1-L5 by comparing the results with those of anatomical studies.

METHODS

Eighty lumbar foramina were studied. First, the best MRI scanning parameters were selected, and the transverse and sagittal axes of each lumbar foramina were scanned to identify and record the ligament-like structures in each lumbar foramen. Then, the cadaveric specimens were anatomically studied, and all ligament structures in the lumbar foramina were retained. The number, morphology and distribution of ligaments under anatomical and MRI scanning were observed. Histological staining of the dissected ligament structures was performed to confirm that they were ligamentous tissues. Finally, the accuracy of ligament recognition in MRI images was statistically analyzed.

RESULTS

A total of 233 foraminal ligaments were identified in 80 lumbar intervertebral foramina through cadaveric anatomy. The radiating ligaments (176, 75.5%) were found to be attached from the nerve root to the surrounding osseous structures, while the transforaminal ligaments (57, 24.5%) traversed the intervertebral foramina without any connection to the nerve roots. A total of 42 transforaminal ligament signals and 100 radiating ligament signals were detected in the MRI images of the 80 intervertebral foramina.

CONCLUSION

The MRI can identify the lumbar foraminal ligament, and the recognition rate of the transforaminal ligament is higher than that of the radiating ligament. This study provides a new method for the clinical diagnosis of the relationship between the lumbar foraminal ligament and radicular pain.

In vivo detection of the lumbar intraforaminal ligaments by MRI

PURPOSE

Intraforaminal ligaments (IFL) are of great interest to anatomists and clinicians to fully understand the detailed anatomy of the neuroforamina and to diagnose unclear radicular symptoms. Studies published until now have described radiological imaging of the IFLs using magnetic resonance imaging (MRI) on donor bodies. In the present study, we investigated the detectability of lumbar IFLs in vivo in adults using the high spatial resolution of the constructive interference in steady state (CISS) sequence.

METHODS

A total of 14 patients were studied using a 1.5 T MRI scanner. The lumbar spine was imaged using the parasagittal CISS sequence, and the detectability of the IFLs was assessed for each lumbar level. All image datasets were analyzed by a radiologist, an orthopedic surgeon, and an anatomist. Interrater reliability was expressed as Fleiss' Kappa. Using a single data set, a three-dimensional (3D) model was created to map the location of the IFLs within the intervertebral foramen (IF) and the immediate surrounding vessels.

RESULTS

Overall, the radiologist was able to detect IFLs in 60% of all imaged IFs, the orthopedic surgeon in 62%, and the anatomist in 66%. Fleiss' Kappa for the various segments varies from 0.71 for L4/5 up to 0.90 for L3/4.

CONCLUSION

Lumbar IFLs were successfully detected in vivo in every patient. The detection frequency varied from 42-86% per IF. We demonstrated reproducible imaging of the IFLs on MRI, with good interrater reliability. The present study was a launching point for further clinical studies investigating the potential impact of altered IFLs on radicular pain.

Structure of Lumbar Intervertebral Foraminal Ligaments Based on 3-Dimensional Reconstruction Through Ultrathin Cryomilling of a Human Cadaver

BACKGROUND

This study aimed to assess the feasibility of using the 3-dimensional (3-D) reconstruction technique based on ultrathin cryomilling to show the lumbar intervertebral foraminal ligaments in situ.

METHODS

Cryomilling was performed on an embalmed human cadaver to acquire successive cross-sectional images. In each of the images, the boundaries of lumbar intervertebral foraminal ligaments and their adjacent structures were outlined, labeled, and reconstructed for 3-D modeling. The morphology, attachments, and spatial orientation of ligaments were described.

RESULTS

A total of 9 ligaments in 10 lumbar intervertebral foramina (IVFs) were identified and reconstructed. These ligaments can be divided into 5 types. The IVFs were divided into 2 or 3 main portions by the first 4 types of ligaments (transforaminal ligaments, corporotransverse ligaments, "reticular" ligaments, and "Y-shaped" ligaments). The radiating ligaments (the fifth type of ligaments) attached to the surrounding structures of the IVF and were connected directly to the nerve root sleeves. Although there was no indication of neurovascular compromise in this normal specimen, these ligaments limit the space within the bony IVF such that under certain pathologic conditions (e.g., inflammation), their presence would make neurovascular compression more likely than if they were absent.

CONCLUSIONS

The 3-D reconstruction technique based on ultrathin cryomilling can effectively show the lumbar intervertebral foraminal ligaments and their anatomical characteristics in situ, providing a new way to clarify the relationships between these ligaments and their adjacent structures.

Magnetic Resonance Imaging Investigation of Cervical-Spine Meniscoid Composition: A Validation Study

OBJECTIVE

The composition of cervical-spine meniscoids may have clinical significance in neck-pain conditions, but the accuracy of assessment of meniscoid composition in vivo using magnetic resonance imaging has not been established. The aim of this study was to compare cervical-spine meniscoid composition by magnetic resonance imaging with histologic composition.

METHODS

Four embalmed cadaveric cervical spines (mean [standard deviation] age, 79.5 [3.7] years; 1 female, 3 male) underwent magnetic resonance imaging, allowing radiologic classification of lateral atlantoaxial- and zygapophyseal-joint (C2-3 to C6-7) meniscoids as either mostly fatty, mixed tissue, or mostly connective tissue. Subsequently, each joint was dissected and disarticulated to allow excision of meniscoids for histologic processing. Each meniscoid was sectioned sagittally, stained with hematoxylin and eosin, examined using light microscopy, and classified as adipose, fibroadipose, or fibrous in composition. Data were analyzed using the kappa statistic with linear weighting.

RESULTS

From dissection, 62 meniscoids were identified, excised, and processed; 46 of these 62 were visualized with magnetic resonance imaging. For single-rater identifying structures, agreement between assessment of meniscoid composition by magnetic resonance imaging and by microscopy was fair (κ = 0.24; 95% confidence interval, 0.02-0.46; P = .02).

CONCLUSION

Findings suggest that the accuracy of this method of magnetic resonance imaging assessment of cervical-spine meniscoid composition may be limited. This should be considered when planning or interpreting research investigating meniscoid composition using magnetic resonance imaging.

Foraminal Ligaments Tether Upper Cervical Nerve Roots: A Potential Cause of Postoperative C5 Palsy

Background  Nerve root tethering upon dorsal spinal cord (SC) migration has been proposed as a potential mechanism for postoperative C5 palsy (C5P). To our knowledge, this is the first study to investigate this relationship by anatomically comparing C5–C6 nerve root translation before and after root untethering by cutting the cervical foraminal ligaments (FL).

Objective  The aim of this study is to determine if C5 root untethering through FL cutting results in increased root translation.

Methods  Six cadaveric dissections were performed. Nerve roots were exposed via C4–C6 corpectomies and supraclavicular brachial plexus exposure. Pins were inserted into the C5–C6 roots and adjacent foraminal tubercle. Translation was measured as the distance between pins after the SC was dorsally displaced 5 mm before and after FL cutting. Clinical feasibility of FL release was examined by comparing root translation between standard and extended (complete foraminal decompression) foraminotomies. Translation of root levels before and after FL cutting was compared by two-way repeated measures analysis of variance. Statistical significance was set at 0.05.

Results  Significantly more nerve root translation was observed if the FL was cut versus not-cut, p  = 0.001; no difference was seen between levels, p  = 0.33. Performing an extended cervical foraminotomy was technically feasible allowing complete FL release and root untethering, whereas a standard foraminotomy did not.

Conclusion  FL tether upper cervical nerve roots in their foramina; cutting these ligaments untethers the root and increases translation suggesting they could be harmful in the context of C5P. Further investigation is required examining the value of root untethering in the context of C5P.

Ligamental compartments and their relation to the passing spinal nerves are detectable with MRI inside the lumbar neural foramina

PURPOSE

Intraforaminal ligaments (IFL) in lumbar neural foramina (NF) and their relation to the lumbar spinal nerves (SN) are addressed.

METHOD

Giemsa- and PAS-stained plastinated body slices of 15 lumbar spines were made and compared to MRI and CT data acquired of the same fresh specimens. We dissected one fixed lumbar spine to discuss our results with previous literature. Macroscopic pathophysiological changes and operational interventions at these lumbar spines were excluded.

RESULTS

In the NF, thin medial IFL touch the SN. As a second compartment, intermedial vertical IFL are seen. A third lateral horizontal compartment of IFL is formed by thick cranial and caudal ligaments. Ligaments of the second and third compartments have no direct contact with the SN. From medial to lateral, the IFL thicken. All compartments are 3D reconstructed. If compartments of the IFL have no direct contact with the SN seen in the slices, a connection was noticed after dissection.

CONCLUSION

Manual dissection seems to be inappropriate for a detailed study of the IFL. The lateral and intermedial compartments being free of the SN may transmit power and protect the SN, while the thin medial IFL may lead the SN passing the NF under physiological conditions. We conclude from the close topographical relation that the IFL may be relevant in foraminal stenosis. Any herniation in the NF presses IFL to the SN. Therefore, we think the IFL themselves could cause neurogenic claudication in case of their non-physiological turnover. Visualisation of IFL seems to be possible by using MRI. These slides can be retrieved under Electronic Supplementary Material.

Morphology and Possible Clinical Significance of the Radiating Extraforaminal Ligaments at the L1-L5 Levels

STUDY DESIGN

A dissection-based study of 10 fresh-frozen human cadavers.

OBJECTIVE

The objective of this study was to identify and describe the radiating extraforaminal ligaments in the exit regions of the L1-L5 intervertebral foramina and to research their possible clinical significance.

SUMMARY OF BACKGROUND DATA

The transforaminal ligaments at the L1-L5 intervertebral foramina have been well studied. However, detailed descriptions of the radiating extraforaminal ligaments at L1-L5 are lacking.

METHODS

Eighty L1-L5 intervertebral foramina from 10 fresh cadavers were studied, and the extraforaminal ligaments were identified. The quantity, morphology, origin, insertion, and spatial orientation of the extraforaminal ligaments in the L1-L5 regions were examined. The length, width, diameter, and thickness of the ligaments were measured using a vernier caliper.

RESULTS

A total of 224 extraforaminal ligaments were identified in the 80 L1-L5 intervertebral foramina, and the occurrence rate of extraforaminal ligaments was 100%. One hundred and eighteen (52.68%) of the extraforaminal ligaments were radiating ligaments, and 106 (47.32%) of the extraforaminal ligaments were transforaminal ligaments. There were 97 (43.30%) ligaments at the superior aspect of the exit regions of the intervertebral foramina, 51 (22.77%) ligaments at the anterior aspect, 44 (19.64%) ligaments at the inferior aspect, and 32 (14.29%) ligaments at the posterior aspect. The morphologies of the extraforaminal ligaments were divided into two types: the strap type and the trabs type.

CONCLUSION

Radiating extraforaminal ligaments exist between spinal nerves and nearby structures. Radiating extraforaminal ligaments may be of clinical importance to surgeons. Dissecting the radiating extraforaminal ligaments before percutaneous endoscopic lumbar discectomy may be an important step in reducing postoperative pain, which may result in significant benefits for patients.

LEVEL OF EVIDENCE

3.

Transforaminal Ligaments of the Lumbar Spine: A Comprehensive Review

Once considered anomalous structures, transforaminal ligaments are not widely known and the criteria for identifying and classifying them are not universal. They are, however, of potential importance during neurological procedures, as their entrapment might lead to radicular pain. Transforaminal ligaments are not present in all patients, but when they are, the incidence of all types of ligaments is significantly higher, with the most common type being the superior corporotransverse ligament. By diminishing the overall amount of space available for the spinal nerve to pass, many early studies concluded that transforaminal ligaments were the cause of nerve root entrapment, resulting in radicular pain. However, more recent studies conducted have claimed that the ligaments do not cause radicular pain but rather are more for the protection of nerves and vessels. The contribution of transforaminal ligaments to radicular pain is still a topic of debate, but their role in the protection of nerves and vessels is certain. The clinician who performs interventional procedures directed toward the intervertebral foramen and the surgeon operating in this region should have a good working knowledge of the anatomy and proposed functions of the transforaminal ligaments.